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Why wind turbine blades are made of composite materials?

I’ve received a question regarding material selection for wind turbines blades. The reader asked why there is a predominance in the use of composite materials for the blades instead of wood, steel and aluminium and other materials used in the first glorious, pioneering years of wind energy.

Please note that I’m by no mean an expert so the only intention of this post is to give a very general introduction to the subject. This is a very broad topic involving different engineering branches.

In general the 2 design drivers are weight and stiffness.

A blade should be as light as possible for a variety of reasons:

To lower gravity induced fatigue loads

To be easily transported and installed

To have a better performance

However, it should also be stiff (that is, rigid) for several other reasons:

To withstand loads (both wind loads and gravity loads). Wind loads are function of wind speed and length of the blade, and increase from the root to the tip of the blade. Gravity loads are function of the material density.

To prevent collision between the blade and the tower under extreme wind

To prevent instability (local or global buckling) maintaining its shape

For these reasons blade designers try to minimize the mass for assigned stiffness levels – it is to find a balance between aerodynamic and structural requirements.

So we want less weight (that is lower density) and more stiffness.

Stiffness is expressed by the Young’s modulus of the material – basically the relationship between force and deformation. In general blades are very flexible, stronger in the flapwise direction and weaker in the edgewise direction.

And here is the reason for the use of composite materials. For a given Young Modulus, the material with the lower density is the composite (resin plus glass fiber).

You can see graphically this relationship in a type of graphic called “Ashby Plot” (I attach a version stolen online from a document of the University of Cagliari.

About Francesco Miceli

Hello! My name is Francesco and I'm a civil engineer specialized in EPC (that is, "turnkey") wind farms projects. I'm currently based in Hamburg, Germany and I'm developing several interesting project all around the world - southern Europe, LATAM and various other countries. If you want to contact me please don't leave a comment in the blog (I don't check them very often) - you can use the contact form. You can write me in English, Spanish and Italian. To find a (somewhat concise) description of my non-wind business activities you can visit my webpage - www.francescomiceli.com If you want to know more about my work, here you can download my CV - www.windfarmbop.com/CV_Francesco_Miceli.pdf Hope you like the blog! Francesco